This application claims the priority of German application 198 82 295.9, filed in Germany on Nov. 12, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an ignition system for an internal combustion engine with at least one spark plug/ignition coil unit inserted into a spark plug shaft of a cylinder head of an internal combustion engine, said unit being connected by electrical leads with the vehicle electrical system.
An ignition system of this kind is known in principle from German Patent Document DE 297 01 235 U. In this document the problem is solved of sealing off the spark plug from the exterior when the spark plug/ignition coil unit located in the cylinder head is provided with a high-voltage lead that passes through the mounting opening of a valve cover placed on the cylinder head. In the known ignition system, a sealing body is provided between the mounting opening and the unit.
However, this exacerbates a problem that generally exists in such an arrangement of a spark plug/coil unit in the cylinder head. Mechanical vibration can cause the ignition coil to rotate relative to the spark plug as the engine operates. This results in a considerable mechanical stress on the electrical lead which in extreme cases can even result in destruction of the lead and hence in complete inoperability of the ignition system, at least for the individual cylinder.
One way of eliminating this problem is to provide a rotary safety device between the ignition core and the spark plug. However, this means considerable structural expense since the connection between the ignition coil and the spark plug is not determined by their relative rotational positions with respect to one another.
A goal of the invention is to provide an ignition system of the type referred to at the outset in which the risk of damaging the electrical connection between the spark plug and ignition coil unit is eliminated in a fashion that employs a simple design.
The invention achieves this goal by providing an ignition system of the type referred to above, wherein a sealing body is located between the coil unit and a mounting opening, said sealing body holding the ignition coil so that it does not rotate and in turn it is held nonrotatably in the mounting opening.
The molded body, which preferably consists of an elastic material, serves primarily to secure the rotational position of the ignition coil. This eliminates a particular mechanical stress on the electrical lead of the ignition coil. It is not necessary to have any kind of rigid mechanical connection between the ignition coil and the spark plug. The correct rotational position of the ignition coil can be achieved by providing an appropriate shape for the molded body. For example, it is sufficient to have a simple marking which corresponds for example with a reference marking on the edge of the mounting opening when the ignition coil is in the correct rotational position.
A design improvement to the invention consists in providing the molded body with an extension that projects over the cross section of the mounting opening and engages a recess. By shaping the ignition coil, it is thus possible for the molded body to fit into the recess when the ignition coil is correctly mounted. The correct seating of the molded body and hence of the ignition coil can thus be recognized easily.
In the known ignition system, ventilation openings are provided inside the sealing body through which the gas volume in the vicinity of the spark plug "breathes". This poses the particular problem of protection against spray. The entrainment of moisture is also associated with the air flow, with the consequential penetration of moisture into the vicinity of the spark plug. On the other hand, a considerable improvement is achieved when a ventilation labyrinth is located inside the molded body. In this way, any moisture that accumulates is shed and the air that may be introduced into the vicinity of the spark plug is free of water drops.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.